Papers by Keyword: Ge Quantum Dots

Abstract: We investigate self-assembled pyramid-shaped Ge Quantum Dots (QDs) with lateral dimensions of 15 nm, and heights of 2.5-3 nm. These Ge QDs were grown by Molecular Beam Epitaxy (MBE) on n-type Si(100) substrates using the Sb-mediated growth mode. The resistivity of the substrates was about 5 Ωcm. The Si buffer layer below the QDs and the Si capping layer above them were doped up to 10¹⁸ cm^-3 by Sb. Cross-section transmission electron microscopy shows the QDs and the Sb delta-doped layers. Using standard photolithographic techniques, a 0.3 mm² Au Schottky contact was applied to the epilayer, while an Ohmic contact was formed on the back side of the substrate. Plotting C^-2 vs. V plot reveals the nominal doping of 10¹⁸ cm^-3. DLTS studies revealed two levels with fitted activation energies of 49 meV and 360-390 meV. They are related to the Sb doping and the Pb interface states, respectively. The simulation suggests a deep level with a volumetric concentration of 2.55×10¹⁵ cm^-3. Multiplying this value by the thickness of the depletion region obtained from the CV measurements, we find that the deep level capture about 5.8×10⁹ electrons per cm².

Abstract: The electrical properties of dome-shaped and pyramid-shaped Ge Quantum Dots (QDs) embedded in p-type Silicon are reported. Capacitance-Voltage (T-CV) characteristics are reported for the temperature range of 35 K to 296 K. The T-CV results showed the desired charge carrier density of the Silicon, on the order of 10¹⁶ cm^-3, at room temperature. Two shoulders are observed in the CV curves between 270 K and 175 K. They are explained as charge stored in the dome- and pyramid-shaped QDs. Below 175 K, only one shoulder is observed in the CV measurements, attributed to charge trapped in dome-shaped QDs. The DLTS study confirms these results. Using a reverse bias between -0.1 V and -1 V two peaks are seen at 50 and 70 K. They are explained in terms of the boron state (the one at 50 K) and charged stored on pyramid-shaped Ge QDs (the one at 70 K). Increasing the reverse bias from -1 V to -1.4 V shows the appearance of a peak around 60 K, attributed to dome-shaped Ge QDs. At the same time, a shoulder appears around 100 K for -1 V, which extends to larger temperatures as the reverse bias magnitude is increased. The activation energies found are around 50 meV (due to Boron), 150 to 250 meV (due to pyramid-shaped Ge QDs), 300 to 350 meV (due to dome-shaped Ge QDs) and 425 meV (due to both dome- and pyramid-shaped Ge QDs).